This invention relates to the production of ethyl chlorothioformate by the reaction of ethyl mercaptan with phosgene in the presence of an activated carbon catalyst, ##STR1## Ethyl chlorothioformate is a useful intermediate for the production of herbicidally effective thiocarbamates. The reaction between ethyl mercaptan and phosgene to produce ethyl chlorothioformate is described in U.S. Pat. No. 3,165,544 of Harry Tilles, which discloses the conduct of this process in laboratory size equipment. It is pointed out that reaction temperatures should be maintained as low as possible, consonant with reasonable reaction rates since at high temperatures the alkyl disulfide by-product begins to form in significant amounts. Maximum temperature is suggested for this reaction using ethyl mercaptan at between about 75.degree. and 140.degree. C.
One process utilized for production of ethyl chlorothioformate by this reaction employs two catalytic beds of activated carbon arranged in series. The first bed is preferably contained in tubes of a multi-tube reactor; the second is in the form of a packed bed reactor containing a single catalyst bed. The first reactor is operated as a continuous liquid phase reactor; more specifically as an upflow tubular catalytic reactor, with starting materials introduced at the bottom and products removed from the upper portion. The partially reacted mixture is then introduced into the top of the second reactor, which functions as a trickle-flow (downflow) packed bed. That is, the second reactor is operated in the continuous gas phase since gaseous hydrogen chloride product is continuously passing upwardly through the bed. Reaction products are removed from the lower portion of the second reactor and passed to downstream apparatus for separating ethyl chlorothioformate. Operation of this process, however, has been found to produce ethyl chlorothioformate in a purity of only between about 91 and about 95%. The major impurity is diethyl disulfide, present in about 3-7%, with most of the remaining impurities being diethyl dithiocarbonate.
It is an object of the present invention to provide an improved process for the production of ethyl chlorothioformate by reaction of ethyl mercaptan and phosgene in the presence of an activated carbon catalyst.
A further objective of the present invention is to provide such a process with minimization of diethyl disulfide by-product.
A third objective of the present invention is to provide such a process with enhanced production capacity.
Yet another object of the present invention is to provide such a process having good temperature control in the reactors.
A still further objective of the present invention is to provide such a process having a good conversion of ethyl mercaptan to ethyl chlorothioformate.